Eco-friendly CO₂ corrosion inhibition on 1Cr steel: Electrochemical and molecular modelling of black tea extract

n this study, the adsorption and chelating properties of black tea extract (BTE) on mild steel were examined in 1 wt% NaCl solution saturated with CO₂ at 40 °C, with inhibitor concentrations ranging from 50 to 4000 ppm. Molecular analysis of BTE was conducted using ultraviolet–visible spectroscopy (UV–Vis), fourier-transform infrared spectroscopy (FTIR) and liquid chromatography-mass spectrometry measurements (LC-MS), while density functional theory (DFT) modelling was used to understand the adsorption energy of various components relative to water. The electrochemical behavior was studied using linear polarization resistance (LPR). In addition, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to analyze the phase composition and morphology of the film formed.

Overall, BTE demonstrated significantly improved corrosion inhibition properties compared to the uninhibited sample. This enhanced performance was evident from its stronger adsorption energy, increased polarization resistance, and higher inhibition efficiency—50 % for 500 ppm and 80 % for 4000 ppm BTE—without degradation over time. DFT modelling revealed that various BTE constituents have a strong affinity for adsorption onto Fe (110), with quercetin exhibiting the strongest adsorption. The interaction between the inhibitor molecules and the steel substrate is primarily physicochemical, with ΔGads = −35 kJ mol⁻¹. Additionally, BTE affected the morphology and chemical composition of the corrosion film, with the inhibited samples showing a chelating layer and a thinner corrosion scale.